It is well-recognized that cancer is a scourge of the modern world, particularly of the developed nations. According to one estimate, in such countries out of a population of 100,000, up to 20,000 people can be expected to contract cancer and fail to get effective treatment. As reported in Vol. 1 of "Dynamics and Opportunities in Cancer Management" by SRI International (1985), page 6, about 5 million persons are likely to die of cancer in 1986. This is particularly devastating in view of the pain and incapacity which precedes actual death by cancer.
It is not surprising, therefore, that much attention is being given to discovering anti-tumor agents. The need for effective anti-tumor agents is so well-known that, whenever it is rumored that one has been found, the press and the public clamor for information.
One problem with conventional chemotherapeutic drugs in the treatment of cancer has been that such drugs tend to be highly toxic to healthy cells as well as to cancer cells. As a result, they produce undesirable side effects, such as alopecia (hair loss), emisis (nausea), nephrotoxicity, cardiotoxicity, etc. Another problem has been the relative lack of success when using even the most popular drugs. For example, "Adriamycin".TM., identified hereinafter, has had only a 14.5% effective response rate in treating stomach cancer in Japan, as reported in Antibiotics Chemother., Vol. 24, pages 149-159 (1978).
Yet, so severe is the problem of cancer that people take such drugs and suffer such side-effects in the hope that the cancer will be alleviated before the side-effects become unbearable. There is currently available some selectivity in toxicity, that is, the ability of the chemotherapeutic agent to selectively kill carcinoma cells instead of healthy cells. However, for most such conventional chemotherapeutic agents that selectivity does not exceed 2 or 3 as defined, for example, by the IC.sub.50 values in in vitro studies of human carcinomas. Such conventional selectivity of 2 or 3 is not adequate because undesirable side effects still plague the patient. Selectivity values defined by the IC.sub.50 ratios of at least 5 to 1 are needed before the selectivity becomes significant enough to predict reduced undesirable side effects.
Therefore, a chemotherapeutic drug having significant selective toxicity to at least some types of cancer is a long-felt need that begs for a solution. This need particularly exists in the arena of differentiated carcinomas, since as explained in Discover, March, 1986, page 37, such constitute about 85% of the cancers. Such carcinomas include cancer of the so-called "hollow" organs: the breast, colon, bladder, lung, prostate, stomach and pancreas. Colon carcinomas are particularly in need of effective chemotherapeutic agents, since at present no known drug is very effective against this cancer. (Discover, March, 1986, pages 36-46, at page 38).
Thiapyryliums, and particularly 2,4,6-triphenylthiapyrylium perchlorates are known to have anti-microbial and anti-phage activities. These are described in e.g., Khim-farm. ZH., Vol. 15, No. 11 pp. 38-40 (1981). However, there is no suggestion anywhere that these thiapyryliums will provide anti-cancer activity.